Problem: $ { {-4} \times \left[\begin{array}{rr}{2} & {1} \\ {-1} & {1} \\ {4} & {-2}\end{array}\right] = {?} } $
Explanation: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{-4}\times{2} & {-4}\times{1} \\ {-4}\times{-1} & {-4}\times{1} \\ {-4}\times{4} & {-4}\times{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-8} & {-4} \\ {4} & {-4} \\ {-16} & {8}\end{array}\right]}$